The invention relates to a method of small-charge blasting, the method comprising drilling, by a rock drill machine, a hole into a material to be excavated, and feeding, after drilling, at least one propellant comprising a propellant charge into the hole by means of a drilling unit. After this, the hole is also sealed before the propellant is ignited. The ignition of the small-charge generates a high gas pressure in the hole, which causes fracturing in the material to be excavated.
The invention further relates to a rock drilling unit for small-charge blasting. The drilling unit comprises a feed beam, a front guide provided in a front part of the feed beam, a rock drill machine, a drilling tool connected with the rock drill machine, and a propellant feed channel which enables a propellant comprising a propellant charge to be fed into a hole formed by the rock drill machine and the drilling tool. The invention still further relates to a front guide which is located in a front part of a feed beam and through which a drilling tool is arranged.
The field of the invention is defined in closer detail in the preambles of the independent claims.
In small-charge blasting, a propellant comprising a propellant charge or a corresponding small-charge is arranged in a hole. Upon ignition of the propellant, a high gas pressure is generated in the hole. The high pressure in the hole causes controlled fracturing in the material to be drilled. An advantage of the small-charge blasting over the conventional explosive blasting is that it is not necessary to move the rock drill machine away from the drilling location for post-drilling ignition, which means that the blasting may be continuous. Further, no strong stress waves are generated in small-charge blasting, wherefore a part of a rock which is not to be broken remains intact and requires no support. In addition, small-charge blasting is safer and it generates less dust.
U.S. Pat. No. 5,308,149 discloses a drilling unit comprising a rock drill machine and a cartridge insertion device which can be indexed by a feed beam. First, a hole is drilled by using the rock drill machine and, subsequently, the cartridge insertion device is indexed to be at the hole for inserting cartridges into the hole. The cartridge insertion device comprises a massive stemming bar by means of which the cartridge is pushed to the bottom of the drilled hole and by means of which the bottom of the hole is also sealed. WO 2006/099 637 discloses an alternative arrangement for small-charge blasting. Besides a rock drill machine, no separate cartridge insertion device is required but cartridges are fed by means of pressurized water to the shank of the rock drill machine and further through the drill rods to the drill bit, wherefrom they are led to the bottom of the hole. A disadvantage of this solution is that the blasting requires custom-made drill rods and drill bits which are to be dimensioned so as to enable the cartridges to be led therethrough.